Hebrews 5:12

For though by this time you ought to be teachers, you need someone to teach you again the first principles of the oracles of God; and you have come to need milk and not solid food.

(We may grow in age but we won't grow spiritually unless we're eating the things of God (The Bible, Prayer, Worship, Discipleship).

It will never happen by osmosis, we have to be hungry for God and intentional in our walk & relationship with Him; not being just hearers of His word, but doers of His Word, & only then we will process commence in becoming spiritually mature.

Remember, spiritual babies, are ones who complain, while the mature is being conformed into the image of Christ.